1. Field of the Invention
The present invention relates in general to an apparatus for controlling an automotive vehicle, more specifically, a vehicle control apparatus for controlling an engine, an automatic transmission and other devices of the vehicle. More particularly, the present invention is concerned with means for preventing an interference between running stability control means and manual transmission shifting control means.
2. Discussion of the Related Art
An automotive vehicle may fall in an unstable running condition, in particular, an unstable turning condition, with the lateral road gripping capacity of a wheel tire being exceeded during turning of the vehicle on a road surface having a relatively low friction coefficient, or at a relatively high speed, or to clear an obstacle, for example. The unstable running condition may be an oversteering or understeering tendency of the vehicle. The oversteering tendency is caused when the road gripping force of the rear wheels is considerably smaller than that of the front wheels, resulting in an excessively larger turning angle of the vehicle than the steering angle, and leading to a spinning tendency of the vehicle. On the other hand, the understeering tendency is caused when the road gripping force of the front wheels is considerably smaller than that of the rear wheels, resulting in a considerably smaller turning angle of the vehicle than the steering angle.
To cope with such running instability of the vehicle, there has been proposed running stability control means in the form of a turning stability control apparatus for stabilizing the vehicle turning behavior, such as a vehicle stability control system (VSC system) as disclosed in JP-A-4-266538. Such a turning stability control apparatus is activated when the vehicle turning condition is unstable, namely, when an oversteering or understeering tendency of the vehicle is detected. Described in detail, the apparatus is adapted to reduce the engine output and at the same time apply a braking force to an appropriate one or ones of the front and rear wheels, for producing a moment that reduces the oversteering or understeering tendency of the vehicle, thereby to stabilize the turning behavior of the vehicle.
The turning stability control apparatus may be further adapted to maintain the automatic transmission in the presently established position or shift up or down the automatic transmission, so as to improve the turning stability of the vehicle. The automotive vehicle equipped with the turning stability control apparatus may also be equipped with manual shifting control means which is adapted to shift the automatic transmission in response to an operation of a manual shifting device while a manual shift mode is selected. This type of vehicle may suffer from some drawbacks due to interferences or inadequate coordination between an operation of the turning stability control apparatus and an operation of the manual shifting control means, in relation to the shifting of the automatic transmission.
For instance, a drawback may arise if the automatic transmission is commanded by the manual shifting control means to shift the automatic transmission by manipulation of the manual shifting device in the manual shift mode while the automatic transmission is commanded by the turning stability control apparatus to maintain the presently established position for improving the turning stability of the vehicle. In this case, the automatic transmission may be shifted according to the command generated by the manual shifting control means, contrary to the command generated by the turning stability control apparatus to hold the automatic transmission in the presently established position.
The manual shifting means may be adapted such that the number of the selectable forward-drive operating positions of the automatic transmission which can be established for forward running of the vehicle can be changed by operation of the manual shifting device in the manual shift mode. Generally, the shift lever has two or more forward-drive positions such as "D", "3" and "2", and the hydraulic control device for the automatic transmission has range positions corresponding to the forward-drive positions of the shift lever. As the shift lever is operated from the position "D" to the position "3" and then to the position "2", the number of the selectable forward-drive operating positions of the automatic transmission is reduced, for example, from "4" to "3" and from "3" to "2". When the manual shifting device is operated, the range position of the hydraulic control device is electrically changed, and the number of the forward-drive operating positions of the automatic transmission is changed. If the manual shifting device is operated to change the number of the selectable forward-drive operating positions of the automatic transmission from "4" to "3", for instance, the automatic transmission may be automatically shifted down from a fourth-speed position to a third-speed position, for example, as in the case where the shift lever is operated from the position "D" to the position "3". Thus, the manual shifting device may be used to indirectly shift down or up the automatic transmission without operating the shift lever, by electrically changing the range position of the hydraulic control device. In this case, too, the vehicle control apparatus suffers from the drawback as described above with respect to the manual shifting means adapted to directly shift the automatic transmission.